Hi Merry -- Nice photo of the kleptoparasite snail & the tubeworm. Your guide (or Lamb & Hanby's book, whatever you were using) got it slightly wrong. The snail doesn't feed on waste products. It steals food particles caught by the worm before the worm can swallow them. Snails that do this grow faster than ones who don't and the worms that are parasitized grow more slowly.Cheers, Leslie